The present invention relates to the field of accommodating different network formats, and more particularly to the field of interworking ATM adaptation layer formats.
Differing delay and bandwidth efficiency requirements, as well as market forces and emerging standards, have led to several different Asynchronous Transfer Mode (ATM) adaptation layers (AALs) for transporting voice or n.times.64 kbps services over ATM. To achieve end-to-end connectivity, however, these AALs need to be "interworked" at some point in the public, private, or customer premises networks.
Presently, AAL-1 is the only standardized AAL for carrying voice and n.times.64 transport, and it does so in three different ways. T1 or E1 circuit emulation; n.times.64 structured data transfer (SDT); or single-call-per-channel (simplified AAL-1). All of these methods have some limitations.
For example, circuit emulation merely provides T1 or E1 transport, and the AAL does not know whether the T1 or E1 contains voice or n.times.64 services. Also, although SDT can be used for multiplexing several voice channels, and in doing so can reduce the cell fill delay by an amount proportional to n (to a minimum of 125 .mu.S), bandwidth inefficiency due to trunking effects can make AAL-1 SDT-based n.times.64 unacceptable in some applications. Finally, simplified AAL-1 specifies how a single voice call or 64 kbps channel is adapted into a single ATM virtual channel, but this introduces approximately 6 msec of delay, making this technique unacceptable in some applications.
Although AAL-1 may have been designed with voice in mind, a data-oriented AAL, AAL-5, resides on ATM network interface cards (NIC) designed for personal computers and workstations. Hence, the market and standards organizations would like to put voice and n.times.64 over AAL-5: This would be a single call per channel with a cell fill of either 32 or 40 bytes. Other proprietary AALs have been designed to optimize two of the following three criteria: delay minimization bandwidth efficiency, and implementation complexity and cost.
U.S. Ser. No. 08/746,176, filed on Nov. 7, 1996, describes a family of AALs with low implementation complexity that offered a range of tradeoffs between bandwidth efficiency and delay minimization. These are shown schematically in FIG. 1.
There is a need, therefore, for a flexible system and process to accommodate voice or 64 kbps services over ATM. There is also a need for such a system and method to provide interworking of such ATM services with standard networks.